Combining channel quality measurements based on sounding reference signals and demodulation reference signals

ABSTRACT

A first communication node communicates by multiple-input-multiple-output (MIMO) wireless communications with a second communication node of a wireless communication system. The method includes receiving a Sounding Reference Signal (SRS) over a plurality of subcarriers transmitted by the second communication node for MIMO communications. Channel quality is measured responsive to the sounding reference signal to output a first channel quality value. A demodulation reference signal is received over a plurality of subcarriers transmitted by the second communication node for MIMO communications. Channel quality is measured responsive to the demodulation reference signal to output a second channel quality value. Reliability of the measurements of the first channel quality value and the second channel quality value is determined. The first and second channel quality values are combined while compensating for the determined reliability difference between the measurements to generate a combined channel quality value. Related communication nodes are disclosed.

RELATED APPLICATIONS

The present application claims the benefit of priority from U.S. patentapplication Ser. No. 13/421,055 entitled “COMBINING CHANNEL QUALITYMEASUREMENTS BASED ON SOUNDING REFERENCE SIGNALS AND DEMODULATIONREFERENCE SIGNALS” filed Mar. 15, 2012, the disclosure of which ishereby incorporated herein in its entirety by reference.

TECHNICAL FIELD

The present disclosure is directed to wireless communications and, moreparticularly, to multiple-input multiple-output wireless communicationsand related network nodes and wireless terminals.

BACKGROUND

In a typical cellular radio system, user equipment units (also referredto as UEs, wireless terminals, and/or mobile stations) communicate via aradio access network (RAN) with one or more core networks. The RANcovers a geographical area which is divided into cell areas, with eachcell area being served by a radio base station (also referred to as anetwork node, a “NodeB”, and/or enhanced NodeB “eNodeB”). A cell area isa geographical area where radio coverage is provided by the base stationequipment at a base station site. The base stations communicate throughradio communication channels with UEs within range of the base stations.

Moreover, a cell area for a base station may be divided into a pluralityof sectors surrounding the base station. For example, a base station mayservice three 120 degree sectors surrounding the base station, and thebase station may provide a respective directional transceiver and sectorantenna array for each sector.

Multi-antenna techniques can significantly increase capacity, datarates, and/or reliability of a wireless communication system asdiscussed, for example, by Telatar in “Capacity Of Multi-AntennaGaussian Channels” (European Transactions On Telecommunications, Vol.10, pp. 585-595, November 1999). Performance may be improved if both thetransmitter and the receiver for a base station sector are equipped withmultiple antennas (e.g., an antenna array) to provide a multiple-inputmultiple-output (MIMO) communication channel(s) for the base stationsector. Such systems and/or related techniques are commonly referred toas MIMO. The LTE standard is currently evolving with enhanced MIMOsupport and MIMO antenna deployments. A spatial multiplexing mode isprovided for relatively high data rates in more favorable channelconditions, and a transmit diversity mode is provided for relativelyhigh reliability (at lower data rates) in less favorable channelconditions.

In an uplink from a UE transmitting from an antenna array over a MIMOchannel to a base station in the sector, for example, spatialmultiplexing (or SM) may allow the simultaneous transmission of multiplesymbol streams over the same frequency from the UE antenna array. Thus,multiple symbol streams may be transmitted from the UE to the basestation over the same downlink time/frequency resource element (TFRE) toprovide an increased data rate.

Similarly, in a uplink from the same UE to the same base station,transmit diversity (e.g., using space-time codes) may allow thesimultaneous transmission of the same symbol stream over the samefrequency from different antennas of the UE antenna array. Thus, thesame symbol stream may be transmitted from different antennas of the UEantenna array to the base station over the same time/frequency resourceelement (TFRE) to provide increased reliability of reception at the basestation due to transmit diversity gain.

The base station and the UE can use adaptive transmission to compensatefor dynamic changes in the channel quality therebetween. The adaptivetransmission can include channel-dependent scheduling, adaptive MIMO,and adaptive modulation and coding scheme (MCS) that is applied totransmissions. In general, the channel quality varies across time (e.g.,frame), frequency (e.g., subcarrier), and space (e.g., antenna port ofthe spaced apart antennas), which implies the use oftime-dependent/frequency-dependent/space-dependent adaptation of thetransmissions.

A limiting factor in the ability to effectively adapt such transmissionsis the need to reliably measure channel quality. A channel qualitymeasurement is typically based on a reference signal (also referred toas a preamble or a pilot) that is transmitted by the UE to the basestation, or vice versa.

Some wireless communication systems adopt several different kinds ofreference signals that are not completely aligned in time, frequency, orspace. Although certain advantages may be obtained if channel qualitycould be estimated using heterogeneous reference signals, the lack oftime, frequency, and/or space alignment of the reference signals cansubstantially degrade the reliability of the resulting channel qualityestimate.

The approaches described in this section could be pursued, but are notnecessarily approaches that have been previously conceived or pursued.Therefore, unless otherwise indicated herein, the approaches describedin this section are not prior art to the claims in this application andare not admitted to be prior art by inclusion in this section.

SUMMARY

It is therefore an object to address at least some of the abovementioned disadvantages and/or to improve performance in a wirelesscommunication system.

Some embodiments of the present invention provide a method of operatinga first communication node is provided. The first communication nodecommunicates by multiple-input-multiple-output (MIMO) wirelesscommunications with a second communication node of a wirelesscommunication system. The method includes receiving a sounding referencesignal over a plurality of subcarriers transmitted by the secondcommunication node for MIMO communications. Channel quality is measuredresponsive to the sounding reference signal to output a first channelquality value. A demodulation reference signal is received over aplurality of subcarriers transmitted by the second communication nodefor MIMO communications. Channel quality is measured responsive to thedemodulation reference signal to output a second channel quality value.Reliability of the measurements of the first channel quality value andthe second channel quality value is determined. The first channelquality value and the second channel quality value are combined whilecompensating for a difference between the determined reliability of themeasurements to generate a combined channel quality value.

In certain embodiments, because the reliability of the channel qualityvalue based on the sounding reference signal and the channel qualityvalue based on the demodulation reference signal is determined, thecombined channel quality value can be generated with higher reliability(e.g., accuracy).

Some embodiments of the present invention provide a first communicationnode that includes an antenna array, a transceiver, and a processor. Theantenna array includes a plurality of MIMO antenna elements. Thetransceiver is coupled to the antenna array, and is configured toreceive communications through the antenna array from a secondcommunication node of a wireless communication system. The receivedcommunications include a sounding reference signal received over aplurality of subcarriers and a demodulation reference signal receivedover a plurality of subcarriers. The processor is coupled to thetransceiver and configured to measure channel quality responsive to thesounding reference signal to output a first channel quality value, andmeasure channel quality responsive to the demodulation reference signalto output a second channel quality value. The processor determinesreliability of the measurements of the first channel quality value andthe second channel quality value, and combines the first channel qualityvalue and the second channel quality value while compensating for adifference between the determined reliability of the measurements togenerate a combined channel quality value.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the disclosure and are incorporated in and constitute apart of this application, illustrate certain non-limiting embodiment(s)of the invention. In the drawings:

FIG. 1 is a block diagram of a communication system that is configuredaccording to some embodiments;

FIGS. 2 and 3 are block diagrams of a UE and a base station,respectively, configured according to some embodiments; and

FIGS. 4-9 are flow charts illustrating operations and methods that canbe performed by base stations and/or wireless terminals according tosome embodiments.

DETAILED DESCRIPTION

The invention will now be described more fully hereinafter withreference to the accompanying drawings, in which examples of embodimentsof the invention are shown. This invention may, however, be embodied inmany different forms and should not be construed as limited to theembodiments set forth herein. It should also be noted that theseembodiments are not mutually exclusive. Components from one embodimentmay be tacitly assumed to be present/used in another embodiment.

For purposes of illustration and explanation only, various embodimentsof the present invention are described herein in the context ofoperating in a RAN that communicates over radio communication channelswith UEs. It will be understood, however, that the present invention isnot limited to such embodiments and may be embodied generally in anytype of communication network. As used herein, a UE can include anydevice that can communicate through one or more wireless RF channel witha communication system, and may include, but is not limited to, a mobiletelephone (“cellular” telephone), laptop/portable computer, tabletcomputer, and/or desktop computer.

In some embodiments of a RAN, several base stations can be connected(e.g., by landlines or radio channels) to a radio network controller(RNC). The radio network controller, also sometimes termed a basestation controller (BSC), supervises and coordinates various activitiesof the plural base stations connected thereto. The radio networkcontroller is typically connected to one or more core networks.

The Universal Mobile Telecommunications System (UMTS) is a thirdgeneration mobile communication system, which evolved from the GlobalSystem for Mobile Communications (GSM), and is intended to provideimproved mobile communication services based on Wideband Code DivisionMultiple Access (WCDMA) technology. UTRAN, short for UMTS TerrestrialRadio Access Network, is a collective term for the Node B's and RadioNetwork Controllers which make up the UMTS radio access network. Thus,UTRAN is essentially a radio access network using wideband code divisionmultiple access for UEs.

The Third Generation Partnership Project (3GPP) has undertaken tofurther evolve the UTRAN and GSM based radio access networktechnologies. In this regard, specifications for the Evolved UniversalTerrestrial Radio Access Network (E-UTRAN) are ongoing within 3GPP. TheEvolved Universal Terrestrial Radio Access Network (E-UTRAN) comprisesthe Long Term Evolution (LTE) and System Architecture Evolution (SAE).

Note that although terminology from 3GPP (3^(rd) Generation PartnershipProject) LTE (Long Term Evolution) is used in this disclosure toexemplify embodiments of the invention, this should not be seen aslimiting the scope of the invention to only these systems. Otherwireless systems may also benefit from exploiting embodiments of thepresent invention disclosed herein. Accordingly, although variousembodiments are described in the context of controlling uplinktransmissions from a UE to a base station based on the LTE standards,the scope of the invention is not limited thereto.

Also note that terminology such as base station (also referred to as anetwork node, eNodeB or Evolved Node B) and UE (also referred to as awireless terminal) should be considering non-limiting and does not implya certain hierarchical relation between the two. In general a basestation (e.g., an “eNodeB”) and a UE may be considered as examples ofrespective different communication nodes that communicate with eachother over a wireless radio channel. While embodiments discussed hereinmay focus on wireless transmissions in an uplink from a UE to a basestation, embodiments of the invention may also be applied, for example,in the downlink.

Example Communication System

FIG. 1 is a block diagram of a communication system that is configuredto operate according to some embodiments of the present invention. Anexample RAN 100 is shown that may be a Long Term Evolution (LTE) RAN.Radio base station nodes (e.g., eNodeBs) 110 may be connected directlyto one or more core networks 130, and/or radio base stations 110 may becoupled to core networks 130 through one or more radio networkcontroller node (RNC) 112. In some embodiments, functions of the RNC 112may be performed by the base stations 110. The base stations 110communicate over wireless RF channels with UEs 120 that are within theirrespective communication service cells (also referred to as coverageareas). The base stations 110 can communicate with one another throughan X2 interface and with the core network(s) 130 through S1 interfaces,as is well known to one who is skilled in the art.

Example UE and Base Station Configurations

FIG. 2 is a block diagram of a UE 120 which is configured according tosome embodiments of the present invention. The UE 120 includestransceiver(s) 202, a processor circuit 200, and a memory device(s) 210containing functional modules 212. The UE 120 may further include otherelements, such as a display 224, a user input interface 222, and aspeaker 220.

The transceiver 202 is configured to communicate with a base station(e.g., network node, Node B) through an antenna array 204 via wirelessair-interface channels according to operations and methods disclosedherein. By providing a plurality of antenna elements in the antennaarray 204, the UE 120 may receive MIMO communications allowing spatialmultiplexing and/or diversity gain as discussed above. A maximum numberof downlink MIMO channels that may be received simultaneously duringmulti-point and/or single-point MIMO by UE 120 may be equal to thenumber of antenna elements included in the antenna array 204.

The processor 200 may include one or more data processing circuits, suchas a general purpose and/or special purpose processor (e.g.,microprocessor and/or digital signal processor). The processor 200 isconfigured to execute computer program instructions from a channeladaptive transmission module 214 among the functional modules 212 of thememory device(s) 210, described below as a computer readable medium, toperform at least some of the operations and methods described herein asbeing performed by a UE in accordance with one or more embodiments ofthe present invention.

The UE 102 may be a mobile telephone (“cellular” telephone), a dataterminal, and/or another processing device with wireless communicationcapability, such as, for example, a desktop computer, a tablet computer,a laptop computer, an electronic book reader, and/or a video gameconsole.

FIG. 3 is a block diagram of a base station 110 configured according tosome embodiments of the present invention, and elements of which may beincluded in a radio network node, such as an evolved Node B, a RNC,and/or other nodes of a communications system. The base station 110 caninclude one or more transceivers 302, a network interface(s) 320, aprocessor 300, and a memory device(s) 310 containing functional modules312.

The transceiver(s) 302 (e.g., 3GPP compliant transceiver) is configuredto communicate with a UE through an antenna array 304 via wirelessair-interface channels according to operations and methods disclosedherein. By providing a plurality of antenna elements in the antennaarray 304, the base station 110 may receive MIMO communications allowingspatial multiplexing and/or diversity gain as discussed above. A maximumnumber of uplink MIMO channels that may be received simultaneously bythe base station 110 may be equal to the number of antenna elementsincluded in the antenna array 304.

The processor 300 may include one or more data processing circuits, suchas a general purpose and/or special purpose processor (e.g.,microprocessor and/or digital signal processor). The processor 300 isconfigured to execute computer program instructions from a channeladaptive transmission module 314 among the functional modules 312 of thememory device(s) 310, described below as a computer readable medium, toperform at least some of the operations and methods described herein asbeing performed by a base station or other network node in accordancewith one or more embodiments of the present invention.

Separate Channel Quality Estimation Using Sounding Reference Signals andDemodulation Reference Signals

Channel quality measurement is often facilitated by the transmission ofa known signal (such a signal referred to generically herein as a“reference signal”), such as a preamble or pilot signal. Particularembodiments of the solutions described herein may utilize both ademodulation reference signal and a sounding reference signal to measurechannel quality. In such embodiments, the demodulation reference signalmay represent any suitable reference signal that may be used by thereceiving node (e.g., base station 110 in the uplink direction) todemodulate traffic received by that node, such as an LTE DeModulationReference Signal (DMRS) in LTE implementations. The sounding referencesignal may represent any reference signal suitable for the receivingnode to use in measuring channel quality and/or for performing otheroperations based directly or indirectly on channel quality (e.g.,channel-specific scheduling, link adaptation). Although the descriptionbelow focuses, for purposes of illustration, on particular exampleembodiments in which the sounding reference signal represents an LTESounding Reference Signal (SRS) and the demodulation reference signalrepresents an LTE DeModulation Reference Signal (DMRS), the describedsolutions may be implemented using any appropriate forms of soundingreference signals and demodulation reference signals.

In accordance with some embodiments, channel quality measurements areperformed using both a sounding reference signal and a demodulationreference signal. Moreover, the channel quality measurements using thesounding reference signal and the demodulation reference signal arecombined while also compensating for the relative reliability of themeasurements.

Channel quality measurement based on a sounding reference signal (e.g.,an LTE SRS in this example embodiment) will be described first. A basestation 110 signals instructions to a UE 120 that controls (configures)the UE transmission of SRS. The instructions from the base station 110define parameters for the SRS transmission that can include periodicityof the transmissions, frequency position of the transmissions (number ofsubcarriers and frequency(ies) of the subcarriers), and/or bandwidth ofthe transmissions. Other parameters and related operations are disclosedby the following 3GPP standards documents: 1) 3GPP TSGRAN E-UTRA;Physical Channels and Modulation, 3GPP TS 36.211, V10.2.0; and 2) TS36.213 TSGRAN E-UTRA; Physical Layer Procedures, 3GPP TS 36.213,V10.2.0.

The base station 110 receives the SRS over the air from the UE 120 andmeasures the channel quality over the subcarriers over which the SRS istransmitted. This channel quality may represent any appropriateindication (actual or estimated) of a quality or strength of a radiochannel between the relevant elements of the communication system and/orof signals received over that channel. For instance, in the exampleembodiment, the base station 110 measures the channel coefficient andthe interference-plus-noise power and, then uses these measurements tocalculate the corresponding signal-to-interference-plus-noise-ratio(SINR) value, or another channel quality value, for each of thesubcarriers over which the SRS is transmitted. The calculated SINRvalues for each of the subcarriers are combined with the previouslycalculated SINR values, while taking into account the Doppler spread.

It is sometimes necessary/desired to calculate the SINR for particularsubcarriers over which the SRS is not transmitted by the UE 120, such aswhen the whole cell bandwidth needs to be measured, for example, inorder to support channel-dependent scheduling.

Denoting the SINR of the q-th subcarrier at the i-th subframe bySINR_(i,q) ^(S), it can be determined by the base station 110, via thechannel adaptive transmission module 314, based on the followingEquation 1:

SINR_(i,q) ^(S)=(1−β_(q))SINR_(i-1,q) ^(S)+β_(q)SINR_(q) ^(S)  (Equation1)

where SINR_(q) ^(S) represents the aforementioned calculated SINR of thecurrent subframe and 0≦β_(q)≦1 represents a frequency-dependentforgetting factor of the q-th subcarrier (where the forgetting factorreduces the influence of older SINR values on a present calculated SINRvalue). The base station 110, via the channel adaptive transmissionmodule 314, can perform scheduling and link adaptation of the i-thsubframe based on the updated SINR SINR_(i,q) ^(S). Referring toEquation 1, it is noted that setting β_(q)=0 corresponds to keeping theprevious SINR (SINR_(i-1,q) ^(S)), whereas setting β_(q)=1 correspondsto overriding the SINR with the calculated SINR (SINR_(q) ^(S)). Inaccordance with some embodiments, the value of β_(q) is determinedaccording to the reliability (accuracy) of the calculated SINR (SINR_(q)^(S)). The term β_(q) can therefore represents a reliability basedscaling value. For example, β_(q) can be set to 1 (β_(q)=1) in responseto determining that the calculated SINR has at least a thresholdreliability (compared to the previously updated SINR (SINR_(i-1,q)^(S)). In this sense, β_(q) can be computed based on the Doppler spreadbetween the subcarriers so that the SINR update in Equation 1 canincorporate multiple measurements from the previous subframes. Likewise,β_(q) should be computed based on the delay spread between thesubcarriers so that the SINR update can cover the subcarriers over whichSRS is not transmitted.

Though SRS has been typically used by base stations for channel qualitymeasurement, in accordance with some present embodiments, a demodulationreference signal (e.g., an LTE DMRS in this example embodiment) is alsoexploited to further improve the accuracy of the channel qualitymeasurement, especially when SRS is not transmitted frequently enough orit is less reliable than DMRS, e.g., because of power control error. Inparticular embodiments, DMRS may always be included within everytransmission slot from a UE 120 for use by a base station 110 fordemodulation purposes (regardless of the configuration of the basestation 110) while SRS may only be transmitted by a UE 120 periodicallyand on defined subcarriers. Consequently, DMRS can be used for channelquality measurement without introducing additional signaling overheadbetween the UE 120 and the base station 110, as opposed to SRS. The SINRof the subcarriers over which DMRS is transmitted can also be calculatedin the aforementioned manner. In other words, the SINR of the q-thsubcarrier at the i-th subframe by SINR_(i,q) ^(D) can be determined bythe base station 110, via the channel adaptive transmission module 314,based on the following Equation 2:

SINR_(i,q) ^(D)=(1−β_(q))SINR_(i-1,q) ^(D)+β_(q)SINR_(q)^(D).  (Equation 2)

Combining Channel Quality Estimates from Sounding Reference Signals withChannel Quality Estimates from Demodulation Reference Signals

The base station 110 is configured, via the channel adaptivetransmission module 314, to combine a channel quality value (such asSINR_(i,q) ^(S) in this example embodiment) from a sounding referencesignal (e.g., an LTE SRS in this example embodiment) with the channelquality value (such as SINR_(i,q) ^(D) in this example embodiment) froma demodulation reference signal (e.g., an LTE DMRS in this exampleembodiment) to derive an equivalent (combined) channel quality value(such as a combined SINR in this example embodiment). The equivalent(combined) channel quality value can provide a more reliable (accurate)channel quality estimate for each subcarrier that is being used tocommunicate in uplink from the UE 120 to the base station 110.

Although various embodiments are described herein the context of thebase station 110 computing channel quality estimates from uplink SRS andDMRS transmission from the UE 120, the UE 120 may be similarlyconfigured, via the channel adaptive transmission module 214, to computechannel quality estimates from downlink SRS and DMRS transmissions fromthe base station 110.

As explained above, in particular embodiments, the SRS is transmittedbased on a defined schedule and on particular subcarriers, while theDMRS is transmitted in each sub-frame for use in demodulating data. Whenthe DMRS happens to share the time and frequency dimension (but, notnecessarily, the space dimension) with SRS, channel measurements canthen be performed on the same subcarriers using both SRS and DMRS. Thederived SINR of the q-th subcarrier at the i-th subframe be denoted bySINR_(i,q). The SINR can then be sequentially updated, for example,based on DMRS first and then updated again based on SRS. The associatedoperations can correspond to replacing SINR_(i,q) ^(S) and SINR_(i-1,q)^(S) by SINR_(i,q) and SINR_(i,q) ^(D), respectively, in (Equation 1),and replacing SINR_(i-1,q) ^(D) by SINR_(i-1,q) in (Equation 2). Inother words, the SINR update can be determined by the base station 110based on the following Equation 3:

SINR_(i,q) ^(D)=(1−β_(q))SINR_(i-1,q)+β_(q)SINR_(q) ^(D)

SINR_(i,q)=(1−β_(q))SINR_(i,q) ^(D)+β_(q)SINR_(q) ^(S).  (Equation 3)

Potential Problems that May Arise by Use of Equations 3 to EstimateChannel Quality

The sequential SINR update is simple enough to reflect the DMRS-basedmeasurement without significant complexity increase. It may improve theaccuracy of channel quality measurement, but the truth is that it is farfrom the optimal way. For example, the SINR update computed by Equation3 can be further computed by the following Equation 4:

SINR_(i,q)=(1−β_(q))²SINR_(i-1,q)+(1−β_(q))β_(q)SINR_(q)^(D)+β_(q)SINR_(q) ^(S)  (Equation 4)

Equation 4 illustrates that, although the SRS and DMRS measurements aremade within the same subframe (“i”), the SRS measurement is consideredmore reliable than the DMRS measurement (Note that 0≦β_(q)≦1, orequivalently, 0≦1−β_(q)≦1). This can be interpreted as (completely orpartially, depending on β_(q)) overriding the DMRS measurement with theSRS measurement.

On the other hand, if the SRS-based SINR update precedes the DMRS-basedSINR update, the SRS measurement is instead overridden by the DMRSmeasurement. Hence, this approach to the sequential SINR update, causesone measurement to always be overridden by the other measurement, moreimportantly, regardless of the reliability of the two measurements. Thismay result in a significant loss of potential gain of joint channelquality measurement, for example, when one measurement is more reliable(more accurately represents an estimation of the particular subchannel)than the other measurement. For example, the DMRS measurement tends tobe more reliable than the SRS measurement when the SRS transmissioninvolves a transmit power change from PUSCH. Furthermore, in the case ofa MIMO system, when DMRS is precoded by the UE 120 with one of thenon-full rank precoder matrices, the DMRS measurement contributes to thecorresponding space index only (i.e., the precoder matrix used forDMRS), since the DMRS measurement simply provides the precoded channel(not the physical MIMO channel) for the base station 110.

Combining Channel Quality Measurements from Sounding Reference Signaland Demodulation Reference Signal While Compensating for Reliability ofthe Measurements

In accordance with at least some embodiments, channel quality isseparately measured using both a sounding reference signal and ademodulation reference signal. However, instead of combining theseparate measurements in a way that is blind to the relative reliabilityof the measurements, the operations for combining the measurements areperformed in a way that compensates for the relative reliability of themeasurements. Thus, for example, when the channel quality measurementfrom SRS is more reliable than the channel quality measurement fromDMRS, the channel quality measurement from SRS has more effect on thecombined channel quality than the channel quality measurement from DMRS.Conversely, when the channel quality measurement from DMRS is morereliable than the channel quality measurement from SRS, the channelquality measurement from DMRS has more effect on the combined channelquality than the channel quality measurement from SRS.

FIG. 4 is a flowchart of operations and methods may be performed by achannel adaptive transmission module and/or another component incombination with a transceiver and antenna array of the base station 110and/or the UE 120 to generate a combined channel quality value frommeasurements of both a sounding reference signal and a demodulationreference signal. More specifically, in the example embodimentillustrated in FIG. 4, the combined channel quality value is generatedfrom measurements of both an LTE SRS and an LTE DMRS. Referring to FIG.4, the SRS is received (block 400) over a plurality of subcarriers. Thechannel quality is measured (block 402) responsive to the received SRSto generate a first set of channel quality values (“CQ-SRS” valueshere). The DMRS is received (block 404) over a plurality of subcarriers,which may or may not be the same plurality of subcarriers over which theSRS was received. The channel quality is measured (block 406) responsiveto the received DMRS to generate a second set of channel quality values(“CQ-DMRS” values here).

The reliability of the measurements for the CQ-SRS values and theCQ-DMRS values is determined (block 408). The determined reliability isan indication of how accurately the CQ-SRS values and the CQ-DMRS valueseach represent the present quality of the channel for one or moredefined subcarriers that are of-interest for being controlled responsiveto the combined channel quality. The reliability of measurement ofCQ-SRS may be determined based on the relative closeness in time,frequency, and/or space of the measured SRS to one or more definedsubcarriers (e.g., the subcarrier which transported the DMRS).Similarly, the reliability of measurement of CQ-DMRS may be determinedbased on the relative closeness in time, frequency, and/or space of themeasured DMRS to the one or more defined subcarriers (e.g., thesubcarrier which transported the DMRS).

In some embodiments, measurement of the channel quality responsive tothe SRS includes generating a Signal-to-Interference-plus-Noise Ratio,SINR, value for each of the plurality of subcarriers of the SRS.Measurement of the channel quality responsive to the DMRS includesgenerating an SINR value for each of the plurality of subcarriers of theDMRS. The reliability of the measurement of the CQ-SRS value can bedetermined based on the reliability of the SINR values for the pluralityof subcarriers of the SRS, and the reliability of the measurement of theCQ-DMRS value can be determined based on the reliability of the SINRvalues for the plurality of subcarriers of the DMRS.

In a further embodiment, determination of the reliability of themeasurement of the channel quality values for the plurality ofsubcarriers of the SRS can include determining the reliability of themeasurement of each of the channel quality values based on a frequencyseparation between a subcarrier of the SRS used to measure thecorresponding channel quality value and at least one subcarrier of thesecond communication node that is controlled by the combined channelquality value (and/or the subcarrier whose channel quality value ismeasured). Similarly, determination of the reliability of themeasurement of the channel quality values for the plurality ofsubcarriers of the DMRS can include determining the reliability of themeasurement of each of the channel quality values based on a frequencyseparation between a subcarrier of the DMRS used to measure thecorresponding channel quality value and at least one subcarrier of thesecond communication node that is controlled by the combined channelquality value (and/or the subcarrier whose channel quality value ismeasured).

In a further embodiment, determination of the reliability of themeasurement of the channel quality values for the plurality ofsubcarriers of the SRS can include determining the reliability of themeasurement of each of the channel quality values based on a timeseparation between timing of the SRS used to measure the correspondingchannel quality value and timing of a data signal from the secondcommunication node. Similarly, determination of the reliability of themeasurement of the channel quality values for the plurality ofsubcarriers of the DMRS comprises determining the reliability of themeasurement of each of the channel quality values based on a timeseparation between timing of the DMRS used to measure the correspondingchannel quality value and the timing of the data signal from the secondcommunication node.

The determination of the reliability of the measurement of the channelquality values for the plurality of subcarriers of the SRS can includedetermining a power difference between the SRS used to measure thecorresponding channel quality value and the data signal from the secondcommunication node.

The reliability of the measurements may be determined relative to eachanother, such as by determining a ratio of the relative reliabilities,instead of being separate determined values. In accordance with someembodiments, the SRS and DMRS share the same time and frequencydimensions, but don't necessarily share the same space dimension.

The CQ-SRS value and the CQ-DMRS value are then combined whilecompensating (block 410) for a difference between the determinedreliability of the measurements to generate a combined channel qualityvalue. As will be explained in further detail below with regard to FIGS.7-9, the compensation (block 410) for the difference between thedetermined measurement reliability may include controlling andoperational order with which the CQ-SRS value and the CQ-DMRS value arecombined (e.g., which value has a greater effect on the combined channelquality value), and/or one or both of the CQ-SRS and CQ-DMRS values maybe scaled based on their relative reliability when being combined togenerate the combined channel quality value.

FIG. 5 is a flowchart of operations and methods that may be performed bythe base station 110 and/or by the UE 120 responsive to the combinedchannel quality value. Referring to FIG. 5, the base station 110 (viathe channel adaptive transmission module 314 and/or via othercomponents) can use the combined channel quality value to control (block500) scheduling transmissions by the UE 120, to control (block 500)selection of the modulation and coding scheme (MCS), and/or to control(block 500) selection of a MIMO transmission mode that is used by the UE120 for transmission to the base station 110. Alternatively oradditionally, the UE 120 (via the channel adaptive transmission module214 and/or via other components) can then use the combined channelquality value to control (block 500) scheduling transmissions by thebase station 110, and/or to control (block 500) selection of themodulation and coding scheme (MCS) and/or the MIMO transmission modethat is used by the base station 110 for transmission to the UE 120.

FIG. 6 is a flowchart of operations and methods that may be performed bythe base station 110 and/or by the UE 120 to control the other node.Referring to FIG. 6, the base station 110 can transmit (block 600) amessage containing information that controls periodicity, frequency,and/or bandwidth of the SRS transmitted by the UE 120. Alternatively oradditionally, the UE 120 can transmit (block 600) a message containinginformation that controls periodicity, frequency, and/or bandwidth ofthe SRS transmitted by the base station 110.

One Approach for Combining Channel Quality Measurements from SoundingReference Signals and Demodulation Reference Signals While Compensatingfor Reliability of the Measurements

In accordance with some embodiments, an approach for combining thechannel quality measurements generated based on a sounding referencesignal and a demodulation reference signal for the present subframe togenerate the combined channel quality measurement value is based onEquation 4, above, but uses the relative reliability of the soundingreference signal and the demodulation reference signal measurements forthe present subframe to control the order with which the soundingreference signal measurement and the demodulation reference signalmeasurement are combined with the channel quality measurement for aprevious subframe.

FIG. 7 is a flowchart of operations and methods that may be performed bythe base station 110 and/or by the UE 120 to generate a combined channelquality measurement based on measurements of both a sounding referencesignal and demodulation reference signal. For ease of explanation only,operations and methods will be described in the context of beingperformed by the base station 110 which measures an SRS and a DMRS inuplink from the UE 120, although this approach is not limited theretoand may be performed by the UE 120 on downlink and/or on any suitableform of sounding reference signal and demodulation reference signal.

Referring to FIG. 7, a determination (block 700) is made as to whetherthe SRS based channel quality measurement (“CQ-SRS”) value is morereliable than the DMRS based channel quality measurement (“CQ-DMRS”)value for a present subframe and subcarrier. The determination mayinclude comparing a ratio of the relative CQ-SRS reliability and CQ-DMRSreliability to a defined value (e.g., 1) and selecting between twooperational branches responsive to the comparison.

When the CQ-SRS measurement is more reliable, the CQ-DMRS value for thepresent subframe is combined (block 702) with a scaled representation ofa previously generated CQ-DRMS value for a previous subframe to generatean updated CQ-DRMS value. The CQ-SRS value is then combined (block 704)with a scaled representation of the updated CQ-DRMS value to generate acombined channel quality value. The combined channel quality value isthen output (block 710) for use in controlling, for example, schedulingof transmissions and/or selection of MCS used for transmissions by theUE 120.

In contrast, when the CQ-DMRS measurement is more reliable, the CQ-SRSvalue for the present subframe is combined (block 706) with a scaledrepresentation of a previously generated CQ-SRS value for a previoussubframe to generate an updated CQ-SRS value. The CQ-DMRS value is thencombined (block 708) with a scaled representation of the updated CQ-SRSvalue to generate a combined channel quality value. The combined channelquality value is then output (block 710).

FIG. 8 is a flowchart of operations and methods that are similar tothose of FIG. 7 explained above, however the channel qualitymeasurements are now specifically related to measuring asignal-to-interference-plus-noise-ratio (SINR) value for each of thesubcarriers over which the SRS is transmitted, and measuring a SINRvalue for each of the subcarriers over which the DMRS is transmitted.Referring to FIG. 8, a SINR value is generated (block 800) from areceived SRS for the i-th subframe and q-th subcarrier according to thefollowing Equation 5:

SINR_(i,q) ^(S)=(1−β_(q))SINR_(i-1,q) ^(S)+β_(q)SINR_(q) ^(S)  (Equation5)

A SINR value is also generated (block 802) from a received DMRS for thei-th subframe and q-th subcarrier according to the following Equation 6:

SINR_(i,q) ^(D)=(1−β_(q))SINR_(i-1,q) ^(D)+β_(q)SINR_(q) ^(D)  (Equation6)

A decision is then made (block 804) whether SINR_(q) ^(S) is morereliable than SINR_(q) ^(D), and, if so, then the combined SINR value isgenerated (block 806) based on the following Equation 7:

SINR_(i,q)=(1−β_(q))²SINR_(i-1,q)+(1−β_(q))β_(q)SINR_(q)^(D)+β_(q)SINR_(q) ^(S)  (Equation 7)

When the decision (block 804) is opposite, the combined SINR value isgenerated (block 808) based on the following Equation 8:

A combined channel quality value (e.g., a combined SINR_(i,q) in thisexample) is then output (block 810) for the i-th subframe and q-thsubcarrier. As explained above, the combined channel quality value canbe used to control adaptive transmission by the base station 110 and/orthe UE 120 to compensate for dynamic changes in the channel qualitybetween the transmitting and receiving network nodes.

Another Approach for Combining Channel Quality Measurements fromSounding Reference Signals and Demodulation Reference Signals WhileCompensating for Reliability of the Measurements

Another approach will now be explained for combining separate channelquality measurements from sounding reference signals and DMRSdemodulation reference signals while compensating for the reliability ofthe measurements to generate a combined channel quality value.

An example MIMO system equipped with N_(t) transmit antennas and N_(r)receive antennas is described below for purposes of explanation of thisapproach. For ease of explanation only, operations and methods will bedescribed in the context of being performed by the base station 110which measures SRS and DMRS in uplink from the UE 120, although thisapproach is not limited thereto and may be performed by the UE 120 ondownlink and/or on any appropriate type of sounding and demodulationreference signals.

FIG. 9 is a flowchart of operations and methods may be performed by thebase station 110 to generate a combined channel quality measurementbased on measurements of both a sounding reference signals (e.g, an LTESRS here) and a demodulation reference signal (e.g., an LTE DMRS).Referring to FIG. 9, it is assumed that both SRS and DMRS aretransmitted at the q-th subcarrier of the i-th subframe, and DMRS isprecoded with one of the rank-R precoder matrices. Denoting theN_(r)×N_(t) channel estimate of the q-th subcarrier for SRS by E_(i)^(S), and the N_(r)×R channel estimate of the subcarrier for DMRS byE_(i) ^(D), the channel estimates can be respectively determined (blocks900, 902) by the following Equations 9:

E _(i) ^(S) =H _(i) +N _(i) ^(S)

E _(i) ^(D) =H _(i) W _(i) ^(D) +N _(i) ^(D),  (Equations 9)

where H_(i) represents the N_(r)×N_(t) actual channel, W_(i) ^(D)represents the N_(t)×R precoder, and N_(i) ^(S) and N_(i) ^(D) representthe N_(r)×N_(t) estimation error and the N_(r)×R estimation error,respectively. The estimation error also includes the error due tocircuit imperfection such as phase distortion between the SRS used forthe SRS used to measure the corresponding SINR value and the data signalto apply the channel quality measurement. In order to incorporate thesetwo measurements properly, the N_(r)×(N_(t)+R) equivalent channelestimate E_(i) is determined by the following Equation 10:

E _(i):=(E _(i) ^(S) E _(i) ^(D)).  (Equation 10)

From Equations 9 and 10, E_(i) is determined by the following Equation10:

E _(i) =H _(i) W _(i) +N,  (Equation 11)

where the N_(r)×(N_(t)+R) equivalent precoder W_(i) and theN_(r)×(N_(t)+R) equivalent noise N is determined by the followingEquations 12:

W _(i):=(I _(N) _(t) W _(i) ^(D))

N:=(N _(i) ^(S) N _(i) ^(D))  (Equation 12)

The approach can then estimate H_(i) from E_(i). In this estimation,H_(i) is the desired variable, and E_(i) is the noisy observation andW_(i) is the known parameter. This can also be viewed as jointmeasurement on the channel estimate level, in contrast with the jointmeasurement on the SINR level in Equation 3. As shown in Equation 9,this enables the DMRS measurement to contribute to the whole space,i.e., the SINR update of the space indices corresponding to all otherprecoder matrices. Note that this is not possible with the conventionalsequential SINR update in Equation 3. Some conventional estimationtechniques that can be used in a new way according to some embodimentsfor the particular estimation operation, include, but not limited to, aleast square (LS) estimation, a maximum likelihood (ML) estimation, anda minimum mean square error (MMSE) estimation. The covariance of N canneed to be estimated for most of the estimation techniques, and it isdetermined by the auto-covariance and the cross-covariance of H_(i) ^(S)and N_(i) ^(D). Through the covariance, a difference between thereliability of the two measurements can be taken into account, when theequivalent channel H_(i) is estimated from Equation 11.

As an example, LS estimation is chosen here. For simplicity, it isassumed that N is zero-mean identically and independently distributedGaussian random matrix. Then the LS estimate Ĥ_(i) is determined by thefollowing Equation 13:

Ĥ_(i)=E_(i)W_(i) ⁺  (Equation 13)

where (•)⁺ represents a pseudo-inverse matrix. For example, when DMRS isprecoded with the full-rank precoder matrix, i.e., W_(i) ^(D)=I_(N) _(t), W_(i) ⁺ is determined by the following Equation 14:

$\begin{matrix}{W_{i}^{+} = {\frac{1}{2}\begin{pmatrix}I_{N_{t}} \\I_{N_{t}}\end{pmatrix}}} & \left( {{Equation}\mspace{14mu} 14} \right)\end{matrix}$

and thus the estimate of H_(i) is nothing but the average of E_(i) ^(S)and E_(i) ^(D).

When the two channel estimates have different reliability, for example,DMRS and SRS experience different power spectral density or differentestimation error, N_(i) ^(S) and N_(i) ^(D) have different covariance,and N is no longer identically and independently distributed Gaussian.However, when a proper estimation technique is used, the reliabilitydifference is taken into account, when the two measurements areincorporated. For example, when the covariances of N_(i) ^(S) and N_(i)^(D) are related by the following Equation 15:

E[vec(N _(i) ^(D))vec^(H)(N _(i) ^(D))]=αE[vec(N _(i) ^(S))vec^(H)(N_(i) ^(S))],  (Equation 15)

the LS estimation is expressed by the following Equation 16:

$\begin{matrix}{{\hat{H}}_{i} = {\left( {E_{i}^{S}\frac{1}{\sqrt{\alpha}}E_{i}^{D}} \right){\left( {I_{N_{t}}\frac{1}{\sqrt{\alpha}}W_{i}^{D}} \right)^{+}.}}} & \left( {{Equation}\mspace{14mu} 16} \right)\end{matrix}$

A reliability scale value α is generated (block 904) based on therelative reliability of the channel measurement from SRS relative to thereliability of the channel measurement from DMRS. When DMRS is precodedwith the full-rank precoder matrix, i.e., W_(i) ^(D)=I_(N) _(t) , acombined channel quality estimate, Ĥ_(i), is determined (block 906) bythe following Equation 17:

$\begin{matrix}{{\hat{H}}_{i} = {\frac{{\alpha \; E_{i}^{S}} + E_{i}^{D}}{\alpha + 1}.}} & \left( {{Equation}\mspace{14mu} 17} \right)\end{matrix}$

Thus the weight of E_(i) ^(S) is scaled by the reliability scale value αcompared to the weight of E_(i) ^(D). In other words, the more reliablemeasurement is considered more importantly than the other measurement.An updated channel estimate value for the q-th subcarrier at the i-thsubframe can be determined (block 908) by the following Equation 18:

Ĥ _(i,q)=(1−β_(q))Ĥ _(i-1,q)+β_(q).  (Equation 18)

A combined channel quality value (e.g., a combined SINR value) can thenbe output (block 910) using the updated channel estimate.

In some embodiments above, the combined channel quality estimate hasbeen determined for subcarriers that include both SRS and DMRS. For thesubcarriers over which either SRS or DMRS (but not both) is transmitted,the conventional (non-sequential) operations of Equations 1 and 2 can beapplied to calculate and update the SINR of the subcarrier. For thesubcarriers over which neither SRS nor DMRS is transmitted, the SINR ofthe subcarriers covered by SRS or DMRS (or both) can be extrapolated tocover the whole cell bandwidth.

Potential Advantages of at Least Some Embodiments

In accordance with at least some embodiments, channel quality isseparately measured using both a sounding reference signal and ademodulation reference signal, and the joint measurements are combinedto generate a combined channel quality estimate. However, instead ofcombining the separate measurements in a way that is blind to therelative reliability of the measurements, the operations for combiningthe measurements are performed in a way that compensates for therelative reliability of the measurements. The combined channel qualityestimate can thereby have improved accuracy. Compensating for therelative reliability of the measurements may be particularlyadvantageous when a demodulation reference signal is precoded with oneof the non-full-rank precoder matrices, because the demodulationreference signal measurement contributes to the SINR update of not onlythe space index used for the demodulation reference signal but also allthe other space indices.

ABBREVIATIONS

DMRS Demodulation Reference Signal

MCS Modulation and Coding Scheme

MIMO Multiple Input Multiple Output

RAN Radio Access Network

SINR Signal to Interference Plus Noise Ratio

SRS Sounding Reference Signal

UE User Equipment Node

Further Definitions and Embodiments

In the above-description of various embodiments of the presentinvention, it is to be understood that the terminology used herein isfor the purpose of describing particular embodiments only and is notintended to be limiting of the invention. Unless otherwise defined, allterms (including technical and scientific terms) used herein have thesame meaning as commonly understood by one of ordinary skill in the artto which this invention belongs. It will be further understood thatterms, such as those defined in commonly used dictionaries, should beinterpreted as having a meaning that is consistent with their meaning inthe context of this specification and the relevant art and will not beinterpreted in an idealized or overly formal sense expressly so definedherein.

When an element is referred to as being “connected”, “coupled”,“responsive”, or variants thereof to another element, it can be directlyconnected, coupled, or responsive to the other element or interveningelements may be present. In contrast, when an element is referred to asbeing “directly connected”, “directly coupled”, “directly responsive”,or variants thereof to another element, there are no interveningelements present. Like numbers refer to like elements throughout.Furthermore, “coupled”, “connected”, “responsive”, or variants thereofas used herein may include wirelessly coupled, connected, or responsive.As used herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. Well-known functions or constructions may not be described indetail for brevity and/or clarity. The term “and/or” includes any andall combinations of one or more of the associated listed items.

As used herein, the terms “comprise”, “comprising”, “comprises”,“include”, “including”, “includes”, “have”, “has”, “having”, or variantsthereof are open-ended, and include one or more stated features,integers, elements, steps, components or functions but does not precludethe presence or addition of one or more other features, integers,elements, steps, components, functions or groups thereof. Furthermore,as used herein, the common abbreviation “e.g.”, which derives from theLatin phrase “exempli gratia,” may be used to introduce or specify ageneral example or examples of a previously mentioned item, and is notintended to be limiting of such item. The common abbreviation “i.e.”,which derives from the Latin phrase “id est,” may be used to specify aparticular item from a more general recitation.

Example embodiments are described herein with reference to blockdiagrams and/or flowchart illustrations of computer-implemented methods,apparatus (systems and/or devices) and/or computer program products. Itis understood that a block of the block diagrams and/or flowchartillustrations, and combinations of blocks in the block diagrams and/orflowchart illustrations, can be implemented by computer programinstructions that are performed by one or more computer circuits. Thesecomputer program instructions may be provided to a processor circuit ofa general purpose computer circuit, special purpose computer circuit,and/or other programmable data processing circuit to produce a machine,such that the instructions, which execute via the processor of thecomputer and/or other programmable data processing apparatus, transformand control transistors, values stored in memory locations, and otherhardware components within such circuitry to implement thefunctions/acts specified in the block diagrams and/or flowchart block orblocks, and thereby create means (functionality) and/or structure forimplementing the functions/acts specified in the block diagrams and/orflowchart block(s).

These computer program instructions may also be stored in a tangiblecomputer-readable medium that can direct a computer or otherprogrammable data processing apparatus to function in a particularmanner, such that the instructions stored in the computer-readablemedium produce an article of manufacture including instructions whichimplement the functions/acts specified in the block diagrams and/orflowchart block or blocks.

A tangible, non-transitory computer-readable medium may include anelectronic, magnetic, optical, electromagnetic, or semiconductor datastorage system, apparatus, or device. More specific examples of thecomputer-readable medium would include the following: a portablecomputer diskette, a random access memory (RAM) circuit, a read-onlymemory (ROM) circuit, an erasable programmable read-only memory (EPROMor Flash memory) circuit, a portable compact disc read-only memory(CD-ROM), and a portable digital video disc read-only memory(DVD/BlueRay).

The computer program instructions may also be loaded onto a computerand/or other programmable data processing apparatus to cause a series ofoperational steps to be performed on the computer and/or otherprogrammable apparatus to produce a computer-implemented process suchthat the instructions which execute on the computer or otherprogrammable apparatus provide steps for implementing the functions/actsspecified in the block diagrams and/or flowchart block or blocks.Accordingly, embodiments of the present invention may be embodied inhardware and/or in software (including firmware, resident software,micro-code, etc.) that runs on a processor such as a digital signalprocessor, which may collectively be referred to as “circuitry,” “amodule” or variants thereof.

It should also be noted that in some alternate implementations, thefunctions/acts noted in the blocks may occur out of the order noted inthe flowcharts. For example, two blocks shown in succession may in factbe executed substantially concurrently or the blocks may sometimes beexecuted in the reverse order, depending upon the functionality/actsinvolved. Moreover, the functionality of a given block of the flowchartsand/or block diagrams may be separated into multiple blocks and/or thefunctionality of two or more blocks of the flowcharts and/or blockdiagrams may be at least partially integrated. Finally, other blocks maybe added/inserted between the blocks that are illustrated, and/orblocks/operations may be omitted without departing from the scope of theinvention. Moreover, although some of the diagrams include arrows oncommunication paths to show a primary direction of communication, it isto be understood that communication may occur in the opposite directionto the depicted arrows.

Many different embodiments have been disclosed herein, in connectionwith the above description and the drawings. It will be understood thatit would be unduly repetitious and obfuscating to literally describe andillustrate every combination and subcombination of these embodiments.Accordingly, the present specification, including the drawings, shall beconstrued to constitute a complete written description of variousexample combinations and subcombinations of embodiments and of themanner and process of making and using them, and shall support claims toany such combination or subcombination.

Many variations and modifications can be made to the embodiments withoutsubstantially departing from the principles of the present invention.All such variations and modifications are intended to be included hereinwithin the scope of the present invention. Accordingly, the abovedisclosed subject matter is to be considered illustrative, and notrestrictive, and the appended claims are intended to cover all suchmodifications, enhancements, and other embodiments, which fall withinthe spirit and scope of the present invention. Thus, to the maximumextent allowed by law, the scope of the present invention is to bedetermined by the broadest permissible interpretation of the followingclaims and their equivalents, and shall not be restricted or limited bythe foregoing detailed description. Any reference numbers in the claimsare provided only to identify examples of elements and/or operationsfrom embodiments of the figures/specification without limiting theclaims to any particular elements, operations, and/or embodiments of anysuch reference numbers.

1. A method of operating a first communication node that communicates bymultiple-input-multiple-output (MIMO) wireless communications with asecond communication node of a wireless communication system, the methodcomprising: receiving a sounding reference signal over a plurality ofsubcarriers transmitted by the second communication node for MIMOcommunications; measuring a channel quality responsive to the soundingreference signal to output a first channel quality value; receiving ademodulation reference signal over a plurality of subcarrierstransmitted by the second communication node for MIMO communications;measuring a channel quality responsive to the demodulation referencesignal to output a second channel quality value; determining areliability of the first channel quality value and a reliability of thesecond channel quality value; and combining the first channel qualityvalue and the second channel quality value while compensating for adifference between the determined reliabilities of the channel qualityvalues to generate a combined channel quality value based on:determining that the measurement of the first channel quality value ismore reliable than the measurement of the second channel quality value,and responding to the determination by combining the second channelquality value for a subframe of the communications from the secondcommunication node with a scaled representation of a previouslygenerated second channel quality value for a previous subframe togenerate an updated second channel quality value, and combining thefirst channel quality value with a scaled representation of the updatedsecond channel quality value to generate the combined channel qualityvalue; and determining the measurement of the second channel qualityvalue is more reliable than the measurement of the first channel qualityvalue, and responding to the determination by combining the firstchannel quality value for a subframe of the communications from thesecond communication node with a scaled representation of a previouslygenerated first channel quality value for a previous subframe togenerate an updated first channel quality value, and combining thesecond channel quality value with a scaled representation of the updatedfirst channel quality value to generate the combined channel qualityvalue.
 2. The method of claim 1, further comprising: controllingscheduling of transmissions by the second communication node, selectionof a modulation and coding scheme used by the second communication node,or selection of a MIMO transmission mode used by the secondcommunication node for transmission responsive to the combined channelquality value.
 3. A method of operating a first communication node thatcommunicates by multiple-input-multiple-output (MIMO) wirelesscommunications with a second communication node of a wirelesscommunication system, the method comprising: receiving a soundingreference signal over a plurality of subcarriers transmitted by thesecond communication node for MIMO communications; measuring a channelquality responsive to the sounding reference signal to output a firstchannel quality value, based on generating a channel estimate for thesounding reference signal of each of a plurality of subcarriers of adefined subframe of the communications from the second communicationnode to output a first plurality of channel quality values; receiving ademodulation reference signal over a plurality of subcarrierstransmitted by the second communication node for MIMO communications;measuring a channel quality responsive to the demodulation referencesignal to output a second channel quality value, based on generating achannel estimate for the demodulation reference signal of each of theplurality of subcarriers of the defined subframe of the communicationsfrom the second communication node to output a second plurality ofchannel quality values; and determining a reliability of the firstchannel quality value and a reliability of the second channel qualityvalue; and combining the first channel quality value and the secondchannel quality value while compensating for a difference between thedetermined reliabilities of the channel quality values to generate acombined channel quality value, based on: generating a plurality ofreliability scale values, each one of the reliability scale values basedon a ratio of the reliability of the measurement of the second pluralityof channel quality values and the reliability of the measurement of thefirst plurality of channel quality values for a different one of thesubcarriers; scaling at least one of the channel estimate for thesounding reference signal and the channel estimate for the demodulationreference signal using the reliability scale value; adding the channelestimate for the sounding reference signal and the channel estimate forthe demodulation reference signal to output a summed channel qualityvalue; and scaling the summed channel quality value using thereliability scale value to generate a combined channel estimate foroutput as the combined channel quality value.
 4. The method of claim 3,further comprising: controlling scheduling of transmissions by thesecond communication node, selection of a modulation and coding schemeused by the second communication node, or selection of a MIMOtransmission mode used by the second communication node for transmissionresponsive to the combined channel quality value.
 5. A firstcommunication node comprising: an antenna array including a plurality ofmultiple-input-multiple-output (MIMO) antenna elements; a transceivercoupled to the antenna array, wherein the transceiver is configured toreceive communications through the antenna array from a secondcommunication node of a wireless communication system, the receivedcommunications including a Sounding Reference Signal (SRS) received overa plurality of subcarriers and a demodulation reference signal receivedover a plurality of subcarriers; and a processor coupled to thetransceiver and configured to: measure channel quality responsive to thesounding reference signal to output a first channel quality value;measure channel quality responsive to the demodulation reference signalto output a second channel quality value; determine reliability of themeasurements of the first channel quality value and the second channelquality value; and combine the first channel quality value and thesecond channel quality value while compensating for the determinedreliability difference between the measurements to generate a combinedchannel quality value based on: determining that the measurement of thefirst channel quality value is more reliable than the measurement of thesecond channel quality value, and respond by combining the secondchannel quality value for a subframe of the communications from thesecond communication node with a scaled representation of a previouslygenerated second channel quality value for a previous subframe togenerate an updated second channel quality value, and combining thefirst channel quality value with a scaled representation of the updatedsecond channel quality value to generate the combined channel qualityvalue; and determining that the measurement of the second channelquality value is more reliable than the measurement of the first channelquality value, and response by combining the first channel quality valuefor a subframe of the communications from the second communication nodewith a scaled representation of a previously generated first channelquality value for a previous subframe to generate an updated firstchannel quality value, and combining the second channel quality valuewith a scaled representation of the updated first channel quality valueto generate the combined channel quality value.
 6. The firstcommunication node of claim 5, wherein the processor is configured to:control scheduling of transmissions by the second communication node,selection of a modulation and coding scheme used by the secondcommunication node, or selection of a MIMO transmission mode used by thesecond communication node for transmission responsive to the combinedchannel quality value.
 7. A first communication node comprising: anantenna array including a plurality of multiple-input-multiple-output(MIMO) antenna elements; a transceiver coupled to the antenna array,wherein the transceiver is configured to receive communications throughthe antenna array from a second communication node of a wirelesscommunication system, the received communications including a SoundingReference Signal (SRS) received over a plurality of subcarriers and ademodulation reference signal received over a plurality of subcarriers;and a processor coupled to the transceiver and configured to: measurechannel quality responsive to the sounding reference signal to output afirst channel quality value, by generating a channel estimate for thesounding reference signal of each of a plurality of subcarriers of adefined subframe of the communications from the second communicationnode to output a first plurality of channel quality values; measurechannel quality responsive to the demodulation reference signal tooutput a second channel quality value by generating a channel estimatefor the demodulation reference signal of each of the plurality ofsubcarriers of the defined subframe of the communications from thesecond communication node to output a second plurality of channelquality values; determine reliability of the measurements of the firstchannel quality value and the second channel quality value; and combinethe first channel quality value and the second channel quality valuewhile compensating for the determined reliability difference between themeasurements to generate a combined channel quality value by: generatinga plurality of reliability scale values, each one of the reliabilityscale values based on a ratio of the reliability of the measurement ofthe second plurality of channel quality values and the reliability ofthe measurement of the first plurality of channel quality values for adifferent one of the subcarriers; scaling at least one of the channelestimate for the sounding reference signal and the channel estimate forthe demodulation reference signal using the reliability scale value;adding the channel estimate for the sounding reference signal and thechannel estimate for the demodulation reference signal to output asummed channel quality value; and scaling the summed channel qualityvalue using the reliability scale value to generate a combined channelestimate for output as the combined channel quality value.
 8. The firstcommunication node of claim 7, wherein the processor is configured to:control scheduling of transmissions by the second communication node,selection of a modulation and coding scheme used by the secondcommunication node, or selection of a MIMO transmission mode used by thesecond communication node for transmission responsive to the combinedchannel quality value.